International Concrete Abstracts Portal

SP82 Contains 38 papers covering the following in situ/nondestructive testing methods: surface hardness and penetration resistance tests; pullout; ultrasonic pulse velocity; break-off; combined methods; maturity techniques. For tests of concrete other than strength: magnetic; electrical; radioactive; pulse echo; radar; microwave absorption; acoustic emission; nuclear; infrared thermography; and permeability methods. A global review of in situ/nondestructive testing is also included.

During the past 40 years in-situ/non-destruc-tive testing of concrete has achieved increasing acceptance for the evaluation of existing concrete structures with regard to their uniformity, durability and other properties. This paper reviews critically the available in-situ/non-destructive tests for estimating concrete strength and for determining properties other than strength, and discusses their implications. The methods discussed for estimating concrete strength in-clude surface hardness and penetration resistance tests, pullout, ultrasonic pulse velocity, break-off, combined methods, and maturity techniques. The tests reviewed for determining properties other than strength include magnetic, electrical, radioactive, pulse echo, radar, microwave absorption, acoustic emission, nuclear, infrared thermography, and permeability methods. Some of the tests described are relatively easy to perform whereas others require sophisticated equipment and trained personnel, and there are others which are still in the development stage. Regardless of the type of test used, it is emphasized that interpretation of test data must be performed by specialists rather than by technicians performing the tests. Unless comprehensive laboratory correlations have been established between the strength parameters to be predicted and the results of in-situ/non-destructive tests, the use of the latter to predict compressive or flexural strength of concrete is discouraged.

The nature of the stress waves found in the Schmidt Hammer after impact during the testing of concrete were examined experimentally. Using a specially designed plunger, the authors have been shown that the impact of the hammer mass produces a large compressive wav e and a large reflected stress waved at r the centre of the plunger. The ratio,or/or of the amplitudes of these waves and the time T between their appearance was found to depend upon the surface hardness of cured concrete. The rebound number was found to be approximately proportional to the ratio of the two stresses and was not significantly affected by the moisture conditions of the concrete. The magnitude of the first stress wave at the centre of the plunger is almost constant and is approximately 80 percent of the value calculated by Smith’s numerical solution, which does not consider the efficiency of the impact of the hammer. The authors have concluded that the principal of operation of the N-type Schmidt test hammer may be more complex than is assumed when consideration is given only to the simple problem of applying Newton’s laws to impacting bodies. It may involve considerable components of longitudinal wave transmission. It is further concluded that, to correctly measure the rebound number of hardened concrete, the Schmidt hammer can be calibrated by testing a material with a constant hardness and measuring the resulting impact stress wave. By observing the behaviour of the impact stress in the plunger the surface hardness of concrete canbe measured with higher accuracy.

This paper summarizes Romanian experience concerning in-situ concrete strength estimation by non-destructive methods. The methods presented include "classical" non-destructive methods such as ultrasonic pulse method and rebound method. The philosophy of transforming the measured property into concrete strength, taking into account concrete composition and maturity, is given. Details about original developments of non-destructive methods for concrete strength estimation are also presented. Such developments are: a) combined SONREB method based on pulse velocity and rebound index measurements, b) sonic coring method, an immersion method using radial transducers, adapted for the inspection of deep foundations, c) acoustic method by shock, a method based on the measurement of the natural period for the quality

The purpose of the present paper is to obtain a practical expression for estimating the compressive strength of concrete the nondestructive testing method combining rebound number evaluation of the -I L L .n strength of concrete members or structures. with ultrasonic pulse velocity and to discuss its applicability to Experimental investigations were carried out to examine the effects of factors such as water-cement ratio, the maximum size and volume fraction of coarse aggregate, the curing condition and age of concrete. Accuracies of the prediction expressed in concrete strength are proposed. The equations are applied for empirical formulae are examined by multiple and practical equations for estimating the evaluating the-strength distribution in a concrete column and in an existing concrete building.